1. Field of the Invention
The present invention relates to a TIR (Total Internal Reflection) prism system for DMD(Digital Micromirror Device) and a projector adopting the same, and particularly, to a TIR prism system for DMD and a projector adopting the same which reduces the loss of incident light, and has a small size and light weight.
2. Description of the Background Art
A projector which is used frequently nowadays is a device for displaying an image using a display element such as an LCD (Liquid Crystal Display) element or a DMD (Digital Micromirror Device), and because it has a small size and light weight, it is distributed widely. Herein, the LCD element has a function of light valve display element, and the DMD has a function of light switch display element.
The DMD is a projection type display element developed by TI (Texas Instruments), US so as to control the light in a DLP (Digital Light Processing) system, and it is a microchip which is made such that a plurality of micromirrors (or micro aluminum mirrors) of 16 xcexcm are planted on a silicon wafer with a 1 xcexcm interval. And a thousand millions of micromirrors may be planted on the microchip.
The thousands millions of micromirrors planted on the microchip are able to display image on a screen by being controlled locations (two modes of on and off) so as to reflect the incident light within the angle of +10xc2x0 through xe2x88x9210xc2x0. Herein, the strength of the light outputted from the DMD is subordinated by the outputting time of the light as a certain angle, and therefore if the outputting time of the light as a certain angle is long, the strength of the light becomes stronger.
General operating characteristics of the DMD will be described as follows.
FIG. 1 is a block diagram showing general operating characteristics of the projector using the DMD, as shown therein, the projector comprises a light source 9 such as a lamp, a DMD 10 receiving the light outputted from the light source 9 and reflecting the incident light as a certain angle according to a certain signal, a projection lens 11 throwing the light reflected from the DMD 10 on a certain screen 15, and an absorption plate 13 for absorbing the light reflected from the DMD 10 at a certain angle but is not incident upon the projection lens 11.
Herein, the DMD 10 includes a blackboard 1, a plurality of electrodes 3 provided on the blackboard 1, digital micromirrors 5 receiving the light outputted from the light source 9 and reflecting the light at a certain angle, and a supporting member 7 for supporting the digital micromirrors 5.
The plurality of electrodes 3 generate an electrostatic field by a voltage signal inputted from outside so as to support movements of the supporting member 7. Then the digital micromirrors 5 of tiny square shape of 16 xcexcm attached on the supporting member 7 are rotated within the angle range of xc2x110xc2x0, and reflects the light inputted from the light source 9 to the projection lens 11 or to the absorption plate 13 in accordance with the rotating angle. The projection lens 11 receives the light reflected from the DMD 10 and projects the light to the screen 15 to display the image thereon.
The operation of the projector constructed as above will be described in more detail as follows.
The digital micromirrors 5 are slanted at a certain initial angle against the plane, when the light outputted from the light source 9 is projected to the micromirrors 5, the digital micromirrors 5 does not reflect the light to the projection lens 11, but reflects to the absorption plate 13. Therefore, the screen 15 becomes black.
And, when a voltage signal is inputted to the plurality of electrodes 3 disposed on the blackboard 1, the plurality of electrodes 3 generates the electrostatic field so as to rotate the supporting member 7 within a certain angle range of +10xc2x0 through xe2x88x9210xc2x0. At that time, the digital micromirrors 5 attached on the supporting member 7 are rotated with the supporting member 7, and therefore the light inputted into the digital micromirrors 5 is reflected to the projection lens 11. When the light inputted into the projection lens 11 is reflected to the screen 15 through the projection lens 11, the screen 15 becomes white.
Therefore, when the voltage signal from outer electric power source to the plurality of electrodes 3, the electrodes 3 generate the electrostatic field so as to rotate the supporting member 7 within the angle of xc2x110xc2x0. Accordingly, the digital micromirrors 5 projects the light outputted from the light source 9 to the screen 15. At that time, the digital micromirrors 5 are rotated at a high speed (on/off operations) according to the inputted motion image signal.
The projector using the DMD of operation characteristics can be divided into a projector of direct reflection type and a projector of TIR prism type, according to input/output type of the light to the DMD.
FIG. 2 is a perspective view showing a projector of direct reflection type for DMD according to the conventional art. As shown therein, the projector includes a light source 19, a color wheel 17 for changing the color of the light outputted from the light source 19 to red, green, and blue and outputting the light, and a DMD 20 receiving the light outputted from the color wheel 17 and reflecting the light to a screen 23. Herein, the DMD 20 is made as a chip and attached on a board 21.
The projector like above displays image on the screen 23 by reflecting the light outputted from the light source 19 using DMD 20. Herein, the color wheel 17 is a wheel having an element which changes the color of the light into red, green, and blue, and outputs it, and is rotated at a certain rotating speed.
However, the projector of direct reflection type is not able to reduce the size of an optical system, and therefore a projector using an optical system such as the TIR prism is developed.
FIG. 3A is a plane view showing a projector using the TIR prism system for DMD according to the conventional art, and FIG. 3B is a perspective view of FIG. 3A. As shown therein, the projector includes a light source 25; a color Wheel 27 changing the color of the light inputted from the light source 25 into red, green, and blue, and outputting the changed color; a stick lens 29 receiving the light outputted from the color wheel 27 and outputting a light of a certain intensity; a first condensing lens 30 for collecting the light outputted from the stick lens 29 and reducing a diameter of the light; a mirror 31 for reflecting the light outputted from the first condensing lens 30 at a certain angle; a second condensing lens 32 for collecting the light outputted from the mirror 31 and outputting the light; a TIR prism system 33 receiving the light outputted from the second condensing lens 32 and outputting the light according to a certain image signal; a DMD 35 controlling the light proceeded inside the TIR prism system 33; and a projection lens 37 receiving the light outputted from the TIR prism system 33 and outputting it to a certain screen 38. Herein, the TIR prism system 33 for DMD 35 will be described in more detail.
FIG. 4A is a perspective view showing the TIR prism system 33 shown in FIG. 3, and FIG. 4B is a side view of FIG. 4A. As shown therein, the TIR prism system 35 includes an incident prism 33-1 receiving the light proceeded from the light source 25 on a certain position P1 on a surface IS5 and total projecting the light (IS4;P2 and IS2;P3); and an outputting prism 33-2 coupled to the incident prism 33-1 at a certain angle, receiving the light transmitted (OS4; P3) from the incident prism 33-1, total reflecting the light inside (OS1; P4 and OS4;P5) without total reflecting when the light is inputted, and then outputting the light (OS2; P6). That is, the incident prism 33-1 and the outputting prism 33-2 are coupled with a tiny gap, therefore the light proceeded from the incident prism 33-1 to the outputting prism 33-2 is not totally reflected on a coupling surface (that is, the surface where the incident prism 33-1 and the outputting prism 33-2 are coupled), and the light inputted into the outputting prism 33-2 is totally reflected on the coupling surface in order to be outputted.
Herein, the referenced dotted line and solid line in the respective surfaces designates a rear surface of the solid view, and the referenced solid line designates a front surface of the solid view.
On the other hand, the DMD 35 attached on a lower surface OS1 of the outputting prism 33-2 totally reflects the light inputted through the lower surface (OS1; P4), and outputs the light through an inclined plane (OS4; P5) of the outputting prism 33-2 and through an outputting surface (OS2; P6).
The incident prism 33-1 and the outputting prism 33-2 included in the TIR prism system 33 will be described in more detail.
FIG. 5A is a perspective view showing the outputting prism 33-2 of the TIR prism system shown in FIG. 4A. As shown therein, the outputting prism 33-2 is a right-angled prism in which the surface OS1 contacted to the DMD and a surface OS2 outputting the light make a right angle, and the inclined plane OS4 for totally reflecting the light reflected from the DMD is included in the outputting prism 33-2.
FIG. 5B is a perspective view showing the incident prism 33-1 of the TIR prism system shown in FIG. 4A. And a manufacturing process of the incident prism 33-1 from a certain right-angled pole will be described as follows.
First, the right-angled pole is cut as a certain angle a1=∠T1T4T3 for a surface IS1, and then the right-angled pole is cut as a certain angle a2=∠T1T2T3. Then, the right-angled pole having the surface IS3 is made. And, the right-angled pole is cut as an angle a3=∠T1T2T6 for a surface IS5, and is cut as an angle a4=∠T4T3T7 for a surface IS2, whereby the incident prism 33-1 is made.
Herein, the angles of the incident prism 33-1 are decided so that the light inputted inside the incident prism is reached to the micromirrors of the DMD after totally reflected, in consideration of rotation directions of the plurality of micromirrors of the DMD (that is, slant direction for an edge of the DMD). Accordingly, the angles of the outputting prism which is coupled to the incident prism are decided.
The projector using the TIR prism system 33-1 and 33-2 fabricated as above displays an image on the screen 38 by controlling the light generated by the light source so as to be projected to the screen 38 through the color wheel 27, the rod lens 29, the first condensing lens 30, the mirror 31, the second condensing lens 33, the TIR prism system 33, the DMD 35, and the projection lens 37.
However, the projector using the TIR prism system of reflection type has a large TIR prism system 33, and the manufactured products have a large size because the DMD is attached on a lower surface of the TIR prism system 33.
Also, the TIR prism system is fabricated so that the light inputted into the incident prism proceeds as a slanted direction against the vertical surface of the proceeding direction and reaches to the DMD in order to be totally reflected to the DMD, and at least four angles are calculated. Therefore, it is difficult to manufacture the prism system, and it needs high cost.
Also, as shown in FIGS. 4A and 4B, since the TIR prism system outputs the light through the processes of transmission P1, a total reflection P2, a transmission P3, a reflection from the DMD P4, a total reflection P5, and transmission P6, and the efficiency of the light energy is lowered.
Therefore, an object of the present invention is to provide a TIR (Total Internal Reflection) prism system for DMD (Digital Micromirror Device) by which a loss of incident light can be reduced.
Another object of the present invention is to provide a projector using the TIR prism system for DMD by which the size and weight of the projector can be reduced.
To achieve these and other advantages in accordance with the purpose of the present invention, as embodied and broadly described herein, there is provided a TIR prism system for DMD, in which the DMD is planted and the light is totally internal reflected in accordance with that the DMD is controlled, comprising: a first prism for receiving the light on a predetermined surface and refracting, and then outputting the refracted light; and a second prism coupled to the first prism for receiving the light outputted from the first prism and transmitting it to the DMD, and totally reflecting and outputting the light according to control of the DMD.
In addition, there is provided a projector using the TIR prism system for DMD comprising: a light source generating and outputting a certain light; light processing units for processing the light outputted from the light source and outputting parallel ray; a TIR prism system for receiving the light outputted from the light processing units and outputting the light gone through 3 transmissions and 1 total reflection; a DMD for controlling a passage of the light so that the light totally reflected can be outputted from the TIR prism system; and a projection lens 370 for receiving the light outputted from the DMD and outputting it to a certain screen.
The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.